Active pulse monitoring in a chemical reactor

ABSTRACT

A method and apparatus for determining changes in a supply system, designed to supply repeated pulses of a vapor phase reactant to a reaction chamber is disclosed. One embodiment involves providing the reactant source, and a gas conduit to connect the reactant source to the reaction chamber, a valve positioned in communication with the reactant source such that switching of the valve induces vapor phase reactant pulses from the reactant source to the reaction chamber and a sensor positioned in communication with the reactant source and configured to provide a signal indicative of a characteristic parameter of the reactant pulse as a function of time. A curve is derived from the signal and the shape of the curve is monitored to determine changes in the curve shape over time during subsequent pulses.

PRIORITY INFORMATION

This application is a continuation of U.S. patent application Ser. No.10/066,169, filed Jan. 30, 2002, which is hereby incorporated byreference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to chemical processes in which aprocessing chemical is supplied in the form of repeated pulses of a gasphase or vapor phase reactant. More particularly, the invention relatesto chemical processes for producing a thin film on a substrate bysubjecting the substrate to repeated pulses of gas or vapor-phasereactants.

2. Description the Related Art

There are several vapor deposition methods for growing thin films on thesurface of substrates. These methods include vacuum evaporationdeposition, Molecular Beam Epitaxy (MBE), different variants of ChemicalVapor Deposition (CVD) (including low-pressure and organometallic CVDand plasma-enhanced CVD), and Atomic Layer Epitaxy (ALE), which is morerecently referred to as Atomic Layer Deposition (ALD).

ALE or ALD is a deposition method that is based on the sequentialintroduction of precursor species (e.g., a first precursor and a secondprecursor) to a substrate, which is located within a reaction chamber.The growth mechanism relies on the adsorption of one precursor on activesites of the substrate. Conditions are such that no more than amonolayer forms in one pulse so that the process is self-terminating orsaturative. For example, the first precursor can include ligands thatremain on the adsorbed species, which prevents further adsorption.Temperatures are maintained above precursor condensation temperaturesand below thermal decomposition temperatures such that the precursorchemisorbs on the substrate(s) largely intact. This initial step ofadsorption is typically followed by a first evacuation or purging stagewherein the excess first precursor and possible reaction byproducts areremoved from the reaction chamber. The second precursor is thenintroduced into the reaction chamber. The second precursor typicallyadsorbs and reacts with the adsorbed species, thereby producing thedesired thin film. This growth terminates once the entire amount of theadsorbed first precursor has been consumed. The excess of secondprecursor and possible reaction byproducts are then removed by a secondevacuation or purge stage. The cycle can be repeated so as to grow thefilm to a desired thickness. Cycles can also be more complex. Forexample, the cycles can include three or more reactant pulses separatedby purge and/or evacuation steps.

ALE and ALD methods are described, for example, in Finnish patentpublications 52,359 and 57,975 and in U.S. Pat. Nos. 4,058,430 and4,389,973, which are herein incorporated by reference. Apparatusessuited to implement these methods are disclosed in, for example, U.S.Pat. No. 5,855,680, Finnish Patent No. 100,409, Material Science Report4(7) (1989), p. 261, and Tyhjiötekniikka (Finnish publication for vacuumtechniques), ISBN 951-794-422-5, pp. 253-261, which are incorporatedherein by reference. ASM Microchemistry Oy, Espoo, Finland, suppliessuch equipment for the ALD process under the trade name ALCVD™.

According to conventional techniques, such as those disclosed in FlPatent publication 57,975, the purging stages involve a protective gaspulse, which forms a diffusion barrier between precursor pulses and alsosweeps away the excess precursors and the gaseous reaction products fromthe substrate. Valves typically control the pulsing of the precursorsand the purge gas. The purge gas is typically an inert gas, for example,nitrogen.

In some ALD reactors, some or all of the precursors may be initiallystored in a container in a liquid or solid state. Such reactors aredisclosed in co-pending U.S. patent applications Ser. No. 09/854,707,filed May 14, 2001, and U.S. Ser. No. 09/835,931, filed Apr. 16, 2001,which are hereby incorporated herein by reference. Within the container,the precursor is heated to convert the solid or liquid precursor to agaseous or vapor state. Typically, a carrier gas is used to transportthe vaporized precursor to the reactor. The carrier gas is usually aninert gas (e.g., nitrogen), which can be the same gas that is used forthe purging stages.

One problem associated with such ALD reactors and other chemicalprocesses that use solid or liquid precursors is that it is difficult todetermine how much solid or liquid precursor is left in the container.For example, low pressure is often required to volatilize the solid orliquid and the precursor may be highly flammable, explosive, corrosiveand/or toxic. As such, the container is usually isolated from thesurroundings except for the gas inlet and outlet conduits during use.Conventional measuring devices positioned in the container can bedamaged and/or are impractical. As such, the chemical process istypically allowed to continue until the supply of precursor isexhausted. Operating in this manner is generally undesirable because itallows the concentration of the precursor in the reactor to drop belowan ideal concentration range when the source is about to becomedepleted. One solution is to calculate the rate of precursor removal.Based upon the calculation, the container can be changed before theprecursor is expected to be exhausted. However, a safety margin istypically including in the calculation. This can result in unusedprecursor remaining in the container, such that refilling is performedprematurely and the reactor downtime is increased (i.e., the duration ofreactor use between refilling is reduced).

Another method for determining how much solid or liquid precursor isleft in a container is disclosed in U.S. Pat. No. 6,038,919. This methodinvolves closing an outlet of the container to define a measurementvolume. A metered amount of gas is delivered to the measurement volume,while the pressure in the measurement volume is monitored. The pressureis used to calculate the amount of precursor remaining in the container.This method also has several disadvantages. For example, it requiresthat the outlet of the container be closed, which increases the downtimeof the reactor.

It is also possible for the various valves and conduits between theprecursor container and the reactor to become damaged or worn out. Thiscan result in contamination and CVD-type reactions between theprecursors, thereby compromising the ALD process. Therefore, a need alsoexists for an improved method and apparatus for determining when thevalves, conduits and connections in an ALD reactor are worn out ordamaged, preferably before worn out or damaged parts lower thethroughput of the reactor.

SUMMARY OF THE INVENTION

One aspect of the present invention involves a method for determiningchanges in a reactant supply system that is designed to supply repeatedpulses of a vapor phase reactant to a reaction chamber. The methodincludes providing a reactant source, a gas conduit system connectingreactant source to the reaction chamber and a valve in the conduitsystem. A sensor also provides a signal indicative of a characteristicparameter of reactant pulses as a function of time. The valve isrepeatedly switched to induce repeated vapor phase reactant pulses, anda curve is generated from the sensor signal, the curve having a shapefor the repeated pulses. The shape of the curve is monitored todetermine changes in the curve shape over time during subsequent pulses.

In an illustrated embodiment, the characteristic parameter is pressure.In another embodiment, the reactant source includes a solid or liquidphase of the reactant.

Another aspect of the present invention involves an apparatus forsupplying repeated pulses of vapor phase reactants to a reactionchamber. The apparatus includes a conduit that connects the reactantsource to the reaction chamber. The apparatus further includes a valve,and a control unit connected to said valve to switch the valverepeatedly such that repeated reactant pulses are created. A sensor ispositioned to measure a characteristic parameter of the reactant pulsesas a function of time, while a diagnostic and control unit isoperatively connected to the sensor and configured to generate a curveof the characteristic parameter of a reactant pulse during repeatedreactant pulses. The diagnostic and control unit monitors or enablesmonitoring the curve shape for detecting changes in the curve shapeduring subsequent reactant pulses.

Yet another aspect of the present invention is a method for determiningchanges in the supply of repeated vapor phase reactant pulses from areactant source within an atomic layer deposition (ALD) system. Themethod includes monitoring a characteristic parameter in a conduit thatcommunicates with a reactant source container in the ALD system. Apattern of the characteristic parameter is compared over time during atleast one cycle to a pattern of the characteristic parameter over timeduring at least one subsequent ALD cycle.

It should be noted that certain objects and advantages of the inventionhave been described above for the purpose of describing the inventionand the advantages achieved over the prior art. Of course, it is to beunderstood that not necessarily all such objects or advantages may beachieved in accordance with any particular embodiment of the invention.Thus, for example, those skilled in the art will recognize that theinvention may be embodied or carried out in a manner that achieves oroptimizes one advantage or group of advantages as taught herein withoutnecessarily achieving other objects or advantages as may be taught orsuggested herein.

It should also be noted that all of these embodiments are intended to bewithin the scope of the invention herein disclosed. These and otherembodiments of the present invention will become readily apparent tothose skilled in the art from the following detailed description of thepreferred embodiments having reference to the attached figures, theinvention not being limited to any particular preferred embodiment(s)disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention will be described in greater detail withthe help of exemplifying embodiments illustrated in the appendeddrawings, in which like reference numbers are employed for similarfeatures in different embodiments and, in which

FIG. 1 is a schematic illustration of an apparatus for supplyingrepeated vapor phase reactant pulses to a reaction chamber according toa first embodiment of the present invention.

FIG. 2 is a schematic illustration of an apparatus for supplyingrepeated vapor phase reactant pulses to a reaction chamber according toa second embodiment of the present invention.

FIG. 3 is a schematic illustration of an apparatus for supplyingrepeated vapor phase reactant pulses to a reaction chamber according toa third embodiment of the present invention.

FIG. 4 is a schematic illustration of an apparatus for supplyingrepeated vapor phase reactant pulses to a reaction chamber according toa fourth embodiment of the present invention.

FIG. 5 is a pressure-time graph also showing a mass flow curve,illustrating pressure and mass flow fluctuations in a solid or liquidsource container during a cyclic ALD process.

FIG. 6 is close up view identifying shape characteristics circled in thepressure flow curve of FIG. 5.

FIG. 7 is a schematic illustration of another apparatus for growing thinfilms onto the surface of a substrate having certain features andadvantages according to another embodiment of the present invention.

FIG. 8 is another pressure-time graph also showing a mass flow curve,illustrating pressure and mass flow fluctuations in a solid or liquidsource container during a cyclic ALD process.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a schematic illustration of an apparatus for supplyingrepeated vapor phase reactant pulses to a reaction chamber according toa first embodiment of the present invention. The system as shown in FIG.1 comprises a reactant source 10, connected through a reactant conduit72 to a reaction chamber 50. The reactant can be present in the reactantsource 10 as a compressed gas or as a vapor phase reactant incommunication with a part of the reactant that is present in liquid orsolid phase, provided that the vapor pressure of the reactant issufficiently high to transport the reactant to the reaction chamber.Gases are removed from the reaction chamber 50 by a vacuum pump 60 viaan outlet conduit 73 and exhausted through a pump exhaust 74. A reactantvalve 30 is placed in the reactant conduit 72 to induce pulse-wisesupply of the reactant to the reaction chamber 50 through repeatedswitching of the reactant valve 30. By repeated and reproducibleswitching of the reactant valve 30 a number of substantially identicalreactant pulses are induced. A flow restrictor 20 may be placed in thereactant conduit 72 to limit the maximum flow of the reactant.

A pulse monitoring apparatus 40 is positioned in communication with thereactant conduit 72, between the reactant valve 30 and the reactionchamber 50. The illustrated pulse monitoring apparatus 40 comprises asensor 42, a diagnostic and control unit 44 and an alarm or a display46. The sensor 42 is configured to generate a signal as a function oftime of a characteristic parameter of the reactant pulses in thereactant conduit 72. The diagnostic and control unit 44 receives thissignal. The sensor 42 is preferably a pressure sensor but other sensorsare also possible, such as, for example, a mass flow meter that is fastenough to be able to measure the pulse mass flow as a function of time,or any other sensor that is capable of measuring a characteristicparameter of the pulse as a function of time.

The diagnostic and control unit 44 generally comprises a general purposecomputer or workstation having a general purpose processor and a memoryfor storing a computer program that can be configured for performing thesteps and functions described below. Part of the memory may be used forstoring measurement data collected by the diagnostic and control unit44. In the alternative, the unit may comprise a hard wired feedbackcontrol circuit, a dedicated processor or any other control device thatcan be constructed for performing the steps and functions describedbelow.

The diagnostic and control unit 44 is preferably operatively connectedto the alarm and/or display device 46, as shown, which may comprise adisplay unit for displaying information gathered by the diagnostic andcontrol unit 44.

During operation of the apparatus as shown in FIG. 1, the sensor 42produces a characteristic repeating pattern of the signal. This patterncan be recorded, stored and/or analyzed by the diagnostic and controlunit 44 and used to determine if changes occur in the supply of pulsesto the reaction chamber. For example, a pressure curve (see, forexample, FIG. 5 and the attending description) can be displayedgraphically on the display unit 46. An operator of the apparatus can usethe display unit 46 to recognize the characteristic repeating pattern ofthe pressure curve. To aid the operator in analyzing the pressure curve,the diagnostic and control unit 44 preferably includes a store anddisplay ability such that data accumulated at different times can becompared. For example, data recorded just after the reactant source 10has been installed can be visually compared to data recorded after thereactant source has been in use for some time.

In a modified embodiment, the diagnostic and control unit 44 can includepattern recognition methodology software configured to characterize theshape of the pressure curve. Using such software, significant deviationsfrom the characteristic shape of the pressure curve can be identifiedand quantified. If such a deviation occurs, an alarm can be activated.An example of such a pattern recognition methodology is the “typicalshape function” methodology, which is described in U.S. Pat. No.5,797,395 and the references identified therein, which are herebyincorporated by reference herein. Such a methodology can be applied overmultiple pulsing series or over a single pulsing series.

In modified arrangements, the diagnostic and control unit 44 can beconfigured to calculate a characteristic parameter of a curve for asingle pulse, such as the average value of the pressure, the peak valueof the pressure, a particular (e.g., maximum or minimum) width of thecurve and/or the area of the curve.

FIG. 2 shows a second embodiment of the present invention whereinsimilar components are indicated with like reference numbers as inFIG. 1. In FIG. 2, the sensor 42 is positioned in communication with theoutlet conduit 73, which connects the reaction chamber 50 with thevacuum pump 60.

FIG. 3 shows a third embodiment of the present invention wherein similarcomponents are indicated with like reference numbers as in FIG. 1. Inthe reactant conduit 72, which connects the reactant source 10 with thereaction chamber 50, a mass flow controller 80 is installed to create asubstantially constant flow of reactant. A bypass conduit 94 isconnected at one end to the reactant conduit 72 and at the other end toan exhaust (not shown). A bypass valve 34 is connected with the reactantvalve 30, through a connection 33 such that the valves 30 and 34 areoppositely switched simultaneously. Consequently, when the reactantvalve 30 is opened, the bypass valve 34 is closed, and when reactantvalve 30 is closed, the bypass valve 34 is opened. The connection 33 canbe operated mechanically, pneumatically or via a control loop.

The invention will now be illustrated by two further examples, whichrelate to liquid or solid reactant sources and employing a carrier gasto transport the reactant from the reactant source to the reactionchamber. FIG. 4 is a schematic illustration of an ALD system 100 havingcertain features and advantages according to the present invention. TheALD system includes the pulse monitoring apparatus 40, which can be usedto monitor the curve shape of repeated reactant pulses and to detect ifchanges in the curve shape occur. The pulse monitoring apparatus 40 isdescribed in the context of an ALD reactor because the pulse monitoringapparatus has particular utility in this context. However, certainfeatures, aspects and advantages of the pulse monitoring apparatus 40described herein may find utility with other types of industrialchemical processes, such as, but not limited to chemical vapordeposition.

As shown in FIG. 4, the illustrated ALD system 100 comprises an inactivegas source 12, a reactant source 16 and a reaction chamber 50 in which asubstrate (not shown) can be positioned. In a more typical ALD system,at least two sources of two mutually reactive reactants are provided andthe substrate is subjected to alternating and repeated pulses of bothreactants. However, for the purpose of illustrating the presentembodiment, only one reactant source is indicated. The inactive gassource 12 provides an inactive gas to facilitate transport of thereactant to the reaction chamber 50 and to purge the reaction chamber50. In the present context, “inactive gas” refers to a gas that isadmitted into the reaction chamber and which does not react with areactant or with the substrate. Examples of suitable inactive gasesinclude, but are not limited to, nitrogen gas and noble gases (e.g.,argon). As is well known in the art of ALD processing, purging of thereaction chamber involves feeding an inactive gas into the reactionchamber 50 between two sequential and alternating vapor-phase pulses ofthe reactants from the reactant source 16 and a second reactant source,not shown. The purging is carried out in order to reduce theconcentration of the residues of the previous vapor-phase pulse beforethe next pulse of the other reactant is introduced into the reactionchamber 50. In other arrangements, the chamber can be evacuated betweenreactant pulses.

In the illustrated arrangement, the same inactive gas, from a singlesource, is used as carrier gas and as purge gas. In alternativeembodiments two separate sources can be used, one for carrier gas andone for purge gas. As will be explained below, the purging gas can alsobe used for providing a gas barrier against the flow of reactantresidues into the reaction chamber 50 during the purging of the reactionchamber 50.

The illustrated reactant source 16 includes a container 17 or similarvessel, which is capable of containing solid and/or a liquid reactantmaterial 18 and in which the reactant material 18 can be vaporized. Itis generally provided with an inlet nozzle (not shown), which isconnected to a carrier gas supply conduit 71 for introduction of acarrier gas into the container 17 from the inactive gas source 12. Thecontainer 17 is also provided with an outlet nozzle (not shown), whichis connected to the reactant conduit 72, which interconnects thereactant source 16 with the reaction chamber 50 through an inlet conduit77. The reactant source 16 can be equipped with a heater (not shown) forvaporizing the reactant material 18. Alternatively, feeding heatedcarrier gas into the reactant source 16 can carry out heating. Oneembodiment of a reactant source container is described in co-pendingU.S. patent application Ser. No. 09/854,706, filed May 14, 2001, theentire contents of which are hereby incorporated by reference herein.

The inactive gas source 12 is also connected to the reaction chamber 50through a purge conduit 91, which is connected to an inlet conduit 77 ofthe reaction chamber 50.

The outlet conduit 73 is connected to the reaction chamber 50 forremoving unreacted vapor-phase reactants and reaction by-products fromthe reaction chamber 50. The outlet conduit 73 is preferably connectedto the evacuation pump 60. The exhaust conduit 74 is connected to theoutlet of the vacuum pump 60.

The illustrated ALD system 100 includes a bypass conduit 94, with afirst end illustrated to the reactant conduit 72 at a point 95 betweenthe reactant gas source 16 and the inlet conduit 77 and a second endconnected to the outlet conduit 73. In a modified arrangement, thebypass conduit 94 can be connected directly to the evacuation pump 60 orto a separate evacuation pump.

In the illustrated arrangement, the conduits described above arepreferably formed from inert material, such as, for example, an inertmetal, ceramic material or glass.

With continued reference to FIG. 4, the mass flow controller 80 and thereactant valve 30 are positioned along the carrier gas supply conduit71. The purging conduit 91 preferably also includes a shut-off valve 34,which in this embodiment will be referred to as the purging valve 34. Aswill be explained below, the reactant valve 30 and the purging valve 34can be used to alternately direct the carrier gas to the reactant source16 and to the purging conduit 91. For this purpose, the reactant valve30 and the purging valve 34 are preferably connected by a connection 33,such that the valves 30 and 34 are oppositely switched simultaneously.Consequently, when the reactant valve 30 is opened, the purging valve 34is closed, and when the reactant valve 30 is closed, the purging valve34 is opened. The connection 33 can be operated mechanically,pneumatically or via a control loop.

Preferably, flow restrictors 21 and 22 are positioned in the purgingconduit 91 and the bypass conduit 94, respectively. The flow restrictors21 and 22 reduce the cross-sectional area of the conduits 91 and 94 anddirect the reactant from the reactant source 16 to the reaction chamber50, rather than into the purging and bypass conduits 91 and 94, during areactant pulse.

The dashed line 52 indicates a hot zone 54 within the ALD system 100.Preferably, the temperature within the hot zone 54 is kept at or abovethe evaporation temperature of the reactant material 18 and preferablybelow the thermal decomposition temperature of the reactants. Dependingupon the reactant, typically the temperature within the hot zone 54 isin the range of about 25 to 500 degrees Celsius. The pressure in thereaction chamber 50 and in the conduits 71, 72, 77, 91, 94 thatcommunicate with the reaction chamber 50 can be atmospheric but moretypically the pressure is below atmospheric in the range of about 1 to100 mbar absolute.

Preferably, the reactant and purging valves 30, 34 are positionedoutside the hot zone 54. That is, within the hot zone 54 there are novalves that can completely close the conduits. The flow restrictors 21and 22, however, can be positioned within the hot zone 54, as shown.Such an arrangement reduces the chances of condensation within the hotzone 54.

According to the illustrated arrangement, the bypass conduit 94 is notclosed by a valve during the pulsing of reactants from the reactantsource 16. As such, during a reactant pulse, a small fraction of theflow of reactant from the reactant source 16 flows into the bypassconduit 94 and into the evacuation pump 60. As such, the flow restrictor22 in bypass conduit 94 is preferably sized such that the flow throughthe bypass conduit 94 is less than about one fifth of that in thereactant conduit 72. More preferably, the flow in the bypass conduit 94is less than about 15%, and most preferably lest than about 10% of thanthe flow in the reactant conduit 72.

With continued reference to FIG. 4, the illustrated ALD systempreferably also includes a purifier 25 for removing impurities, such as,for example, fine solid particles and liquid droplets from the reactantsource 16. The separation of such impurities can be based on the size ofthe particles or molecules, the chemical character and/or theelectrostatic charge of the impurities. In one embodiment, the purifier25 comprises a filter or a molecular sieve. In other embodiments, thepurifier 25 comprises an electrostatic filter or a chemical purifiercomprising functional groups capable of reacting with specific chemicalcompounds present (e.g., water in precursor vapors). Preferably, thepurifier 25 is positioned along the reactant conduit 72 between thereactant source 16 and the reaction chamber 50. More preferably, thepurifier 25 is positioned along the reactant conduit 72 at a pointbetween the reactant source 16 and the connection 95 with the bypassconduit 94. In this manner, the vapor flows in one direction only overthe purifier 25 and the gas phase barrier is formed between the purifier25 and the reaction chamber 50.

The ALD system 100 is preferably operated as follows. For a reactantpulse, the reactant valve 30 is opened while the purging valve 34 isclosed. Inactive carrier gas flows through the reactant source 16wherein the solid or liquid reactant 18 is vaporized such that a vaporexists in the container 17 above the solid or liquid reactant. Thus,reactant 18 from the reactant source 16 is carried in vapor form by thecarrier gas through the reactant conduit 72 and the purifier 25 throughthe inlet conduit 77 into the reaction chamber 50. There is also a smallflow of inactive carrier gas and reactant vapors into bypass conduit 94.

During a purging pulse, the reactant valve 30 is closed while thepurging valve 34 is opened. Purging gas, therefore, flows first throughthe purging conduit 91 and then through the reaction chamber inletconduit 77 into the reaction chamber 50. Moreover, a gas phase barrieris formed in a portion 172 of the reactant conduit 72 between the point95 and the inlet conduit 77 as some of the purging gas flows into thereactant conduit 72 from the purging conduit 91 via inlet conduit 77.This purging gas also flows into the bypass conduit 94 and into theevacuation pump 60. As such, the flow direction of gas is reversed forthe portion 172 of the reactant conduit 72 located between the inletconduit 77 and the bypass conduit 94.

The reactant residues withdrawn via the bypass conduit 94 can berecycled. In such a modified arrangement, the bypass conduit 94 isconnected to a condensation vessel maintained at a lower pressure and/ortemperature in order to provide condensation of vaporized reactantresidues.

The system 100 described above can be extended to include a secondreactant source. In such an arrangement, a second reactant source can bepositioned within a conduit system in a manner similar to that describedabove. Such an arrangement is described in co-pending U.S. patentapplication Ser. No. 09/835,931, filed Apr. 16, 2001, which is herebyincorporated by reference herein. Of course the ALD system 100 can alsobe expanded to more than two reactant sources in light of the disclosureherein.

As mentioned above, one problem associated with ALD systems such as theALD system 100 described above and other chemical processes that usevaporized liquid and/or solid reactants is that it is difficult todetermine how much solid and/or liquid reactant is left in the reactantcontainer 17. The solid or liquid reactant may be highly flammable,explosive, corrosive and/or toxic. As such, the reactant container 17 istypically sealed during use. Conventional measuring devices positionedin the reactant container can be damaged and/or are impractical. Assuch, the chemical process is typically allowed to continue until thesupply of liquid or solid reactant in the reactant container isexhausted. Operating in this manner is generally undesirable because itallows the concentration of the reactant in the reactor to drop below anideal concentration range when the source is about to become depleted ofthe reactant. One solution is to calculate the rate of reactant removalfrom the reactant container. Based upon the calculation, the containercan be changed before the reactant is exhausted. However, a safetymargin is typically included in the calculation. This can result inunused precursor remaining in the container.

The various valves and conduits in the ALD system or chemical processingsystem can become damaged or worn out. This can result in contaminationbetween the precursors thereby compromising the ALD or chemical process.Therefore, a need also exists for an improved method and apparatus fordetermining when the valves, conduits and connections in are worn out,damaged or clogged, preferably before the throughput of the reactorsuffers from any malfunction of the source system.

As shown in FIG. 4, the illustrated system includes the pulse monitoringapparatus 40, which can be used to determine if the curve shape changesin the course of a plurality of reactant pulses. If this is the case,most likely the supply of reactant to the reaction chamber has changed.In this way any change in the system will be detected immediately, suchas a low level of reactant in the reactant vessel, malfunctioning valvesor conduits, so that prompt action can be taken without productionlosses due to poor process performance. The pulse monitoring apparatus40 comprises a pressure sensor 42, which is preferably in communicationwith the carrier gas supply conduit 71 at a position upstream of thereactant valve 30. Although in this way reactant pulses are measuredless directly than when the sensor is mounted, e.g., downstream of thereactant valve 30, it has the advantage that the sensor 42 is notexposed to the reactant material 18.

The pressure sensor 42 generates signal that is indicative of acharacteristic parameter of the pulse, such as, pressure, within thecarrier gas conduit 71. This signal is received by a diagnostic andcontrol unit 44, which is operatively connected to the pressure sensor42. As mentioned above, the diagnostic control unit 44 generallycomprises a general purpose computer or workstation having a generalpurpose processor and the memory for storing a computer program that canbe configured for performing the steps and functions described below. Inthe alternative, the unit can comprise a hard wired feed back controlcircuit, a dedicated processor or any other control device that can beconstructed for performing the steps and functions described below.

The diagnostic and control unit 44 is preferably is operativelyconnected to an alarm and/or display device, which can comprise adisplay unit for displaying information gathered by the diagnostic andcontrol unit 44.

An embodiment of a process for determining the amount of liquid and/orsolid phase reactant 18 in the reactant source 16 will now be describedwith particular reference to FIGS. 5 and 6 and to the equipment of FIG.4. FIG. 5 includes a pressure curve 102, which indicates the pressure asa function of time in the carrier gas conduit 71 as indicated by thepressure sensor 42 (FIG. 4). FIG. 5 also includes a mass flow curve 112,which indicates the mass flow as a function of time through the reactantconduit 72 as indicated by a mass flow meter 81 (FIG. 4) that can beinserted into reactant conduit 72 upstream of the purifier 25. Such amass flow meter 81 is typically not inserted into the ALD system 100during normal operations but is instead preferably used only forexperimental or diagnostic purposes.

During a reactant pulse, the reactant valve 30 is opened while thepurging valve 34 is closed. As such, carrier gas flows through thecarrier gas conduit 71 into the reactant source 16. This causes the massflow as indicated by the mass flow meter 81 to rise, as indicated by thereoccurring peaks 114 in the mass flow curve 112. Correspondingly, thepressure tends to decrease as the carrier fluid is allowed to flow intothe reactant source 16, which has a significant volume and is connectedto the reaction chamber 50 through conduits with a relatively highconductance (i.e., relatively few flow restrictions). This decrease inpressure is indicated by the reoccurring valleys 106 in the pressurecurve 102.

During a purging pulse, the reactant valve 30 is closed while thepurging valve 34 is opened. Purging gas, therefore, flows through thepurging conduit 91 into the reaction chamber 50 through the reactionchamber inlet conduit 77. The reactant valve 30 prevents carrier gasfrom flowing from the carrier gas source 12 into the reactant source 16.As such, as shown in FIG. 5, the mass flow as indicated by the mass flowmeter 81 decreases, as indicated by the reoccurring valleys 116 in themass flow curve 112. Moreover, because the carrier gas can only flowthrough the purge conduit 91, which has a relatively low conductance(i.e., a relatively large amount of flow restrictions) due the presenceof the flow restrictor 21, the pressure as indicated by the pressuresensor 42 increases, as illustrated by the reoccurring peaks 104 in thepressure curve 102.

As such, during the operation of the ALD system 100, the pressure curve102 produces a characteristic repeating pattern as shown in FIG. 5 forthe reactant and purging pulses. This pattern can be recorded, storedand/or analyzed by the diagnostic and control unit 44 and used todetermine when the amount of reactant 18 in the reactant source 16 islow and/or a valve or conduit of the ALD system is damaged or if anyother significant change in the system has occurred. For example, thepressure curve 102 can be displayed graphically on the display unit 46.An operator of the ALD system 100 can use the display unit 46 torecognize the characteristic repeating pattern of the pressure curve102. In particular, the operator can recognize the characteristic shapeof the valleys 106 of the pressure curve 102 for one or more reactantand/or purging pulses. For example, deviations from the establishedpattern would indicate a low level of reactant and/or a damaged valveand/or conduit. To aid the operator in analyzing the pressure curve 102,the diagnostic and control unit 44 preferably includes a store anddisplay ability such that data accumulated at different times can becompared. For example, data recorded just after the reactant source 16has been installed can be visually compared to data recorded after theALD system 100 has been operating for some time.

In a modified embodiment, the diagnostic and control unit 44 can includepattern recognition methodology software configured to characterize theshape of the pressure curve 102 over one or more purging and/or reactantpulses. Using such software, significant deviations from thecharacteristic shape of the pressure curve 102 can be identified andquantified. If such a deviation occurs, an alarm can be activated. Notethat the data can also be manipulated (e.g., summed or integrated overone or a predetermined number of sequential pulses, etc.) prior tocomparison in a manner to accentuate any deviations.

In a modified arrangement, the diagnostic and control unit 44 can beconfigured to calculate the average pressure in the carrier gas conduit71 during one or more reactant and/or purging pulses. In general, as thereactant in the reactant source is depleted, the average pressure in thecarrier gas conduit 71 decreases because there is less resistance to theflow of carrier gas through the reactant container 17. In such anarrangement, the diagnostic and control unit can be configured toindicate that the reactant container 17 needs to be changed when theaverage pressure during a reactant pulse (or during a predefined numberof sequential pulses) drops below a predetermined value.

FIG. 7 illustrates another modified arrangement of a simplified ALDapparatus 100 wherein like numbers are used to refer to parts similar tothose of FIG. 4. As with the previous arrangement, the pulse monitoringapparatus 40 includes a pressure sensor 42, preferably located upstreamof reactant valve 30, a diagnostic control unit 44 and an alarm and/ordisplay device 46. The pulse monitoring apparatus 40 includes a massflow meter 82, which is preferably positioned along the purge conduit91. This position of the mass flow meter 82 is preferred because a massflow meter typically represents a large flow restriction. Placing alarge such flow restriction downstream of the reactant source isgenerally undesirable because the resultant pressure drop across themass flow meter can cause undesirable condensation of the reactant.

FIG. 8 illustrates a pressure curve and mass flow curve, which can begenerated by the diagnostic and control unit 44. The reference numbers202 and 212 represent the pressure and the mass flow curves,respectively, during a series of reactant and purging pulses, asmeasured by the pressure sensor 42 (FIG. 7) and the mass flow meter 82(FIG. 7). As compared to FIG. 5, the mass flow curve 212 is horizontally“shifted” with respect to the pressure curve 202. That is, duringreactant pulses, the mass flow through the purge conduit 91 is small. Incontrast, during purging pulses, the mass flow through the purge conduit91 is large. Accordingly, valleys 206 in the pressure curve 202correspond to valleys 216 in the mass flow curve 212 (both representingreactant pulses) and peaks 204 in the pressure curve 202 correspond topeaks 214 in the mass flow curve 212 (both representing purging pulses).

In this arrangement, the diagnostic and control unit 44 is preferablyconfigured to analyze the patterns of both the pressure curve 202 andthe mass flow curve 212 during one or more purging and/or reactantpulses. Changes in the pattern of the pressure curve 202 indicate thatthe amount of reactant in the reactant container 17 is changing. If thepattern of the pressure curve 202 changes beyond a predetermined value,this indicates that it is time to change the reactant container 17. Incontrast, if the pattern of both the mass flow curve 212 and thepressure curve 202 change beyond a predetermined value, this canindicate that either one of the valves (e.g., the pulsing valve 30)and/or one of the conduits is damaged.

Although the invention has been described in the context of ALD, withliquid and/or solid phase reactants, it will be understood that theinvention is also applicable outside the context of ALD and is alsoapplicable to gaseous reactant sources. In case of a gaseous reactantsource a carrier gas might not be needed.

Further, the sensor to measure a characteristic parameter of thereactant pulse can be a sensor other than a pressure sensor, such as aconcentration sensor, a mass flow sensor or any other sensor, includinga Pirani gauge and a convection gauge, that is capable of characterizingthe pulse(s) and is fast enough to be able to measure a characteristicparameter as a function of time with sufficient resolution.

A convection gauge is similar to the Pirani gauge, but measures theresistivity of a wire (e.g., a gold-plated tungsten wire) to detect thecooling effects of both conduction and convection, and thereby extendsthe sensing range as compared to the Pirani gauge. At higher vacuums,response depends on the thermal conductivity of the gas within which thewire is positioned, while at lower vacuums it depends on convectivecooling by the gas molecules. The resistivity of the filament changeswhen the temperature of the filament changes. The thermal capacity fromthe filament depends on the pressure and thermal conductivity (orthermal capacity) of the surrounding gas atmosphere. As long as theconcentration (partial pressure) of the reactant is the same from onepulse to another, the shape of a current-time curve (for constantvoltage) or voltage-time curve (for constant current) will be unchanged.When the source is about to become depleted, the partial pressure of thereactant decreases and the shape of the curve changes. The measurementrange is typically from 10⁻³ Torr to 1,000 Torr. With the exception ofits expanded range, features and limitations of this sensor are the sameas those of Pirani and most thermocouple gauges. As the pulse repetitionfrequency is in the order of once per second, the time resolution of thesensor should be in the order of I millisecond or better. The sensor canalso be installed at different locations, such as downstream of thereactant source or even downstream of the reaction chamber. Each processsystem will have various suitable locations to install a sensor formeasuring a characteristic parameter of a reactant pulse, which will beclear to someone skilled in the art or can be determined by routineexperimentation. Furthermore it is possible to install several sensorsat more than one location in the system to obtain more completeinformation about the reactant supply.

In yet a further embodiment, a vibration pulse of a switching valve(e.g., valves 30 and 34) is recorded and monitored. A pulsing valvemakes a characteristic vibration, such as within the sonic range, whenit is operating properly. As the valve wears out over time, the soundchanges. A microphone may be attached to the valve body and the sound isrecorded. A spectral analysis of the sound and a comparison topreviously recorded sound pulses allows one to monitor changes in theoperation of the valve as a function of time. A filter can be applied tofilter out a constant level of background sound or incidental backgroundsound so that only the repeating sound pulse of the switching valve ispassed by the filter and analyzed. A significant change in pulse soundcould indicate that it is time to replace the switching valve. In amodified arrangement, instead of monitoring the sound of the valve, thevibrations of the valve can be monitored via a vibration or accelerationsensor. In another modified arrangement, the vibrations of the valve canbe monitored with an acceleration or vibration sensor that creates avoltage output. These sensors can be micro-machined on silicon so theyare quite small and sensitive. In a similar embodiment, the sound orother vibrations from a vacuum pump can be monitored over time with thepurpose to detect changes as a function of time. The vacuum pump doesnot normally create sound pulses or vibration pulses but it has acontinuous mode of operation and as such it differs from the pulsemonitoring described above. Nevertheless, abnormalities can be detectedin the form of changes over time in the curve of the parameter beingmonitored.

In the above-noted embodiments and modifications directed to determiningwhen a solid or liquid source is becoming exhausted such as to effectthe level of reactant in each pulse, the system can also be modified toextend the length of operation before recharging the reactant sourcewithout sacrificing the uniformity of reactant provided per pulse.Through routine experimentation, relationships can be establishedbetween changing patterns in the characteristic parameter(s) and thechanging amount of reactant provided per pulse. Compensating changes inthe reactant pulse duration, for example, can be correlated to thechanges in the characteristic parameter(s). Accordingly, a feedback loopcan be provided between the sensor and the control system for the valvepulsing such that, upon a detected change in the curve(s) in thecharacteristic parameter(s), the switching of the valve is changed suchthat the pulses provide an intended amount of reactant. As an example,when the curve height or the curve area tend to become smaller, the“open” time of the reactant valve can be increased such that the curveregains its original height or- area.

It should be noted that certain objects and advantages of the inventionhave been described above for the purpose of describing the inventionand the advantages achieved over the prior art. Of course, it is to beunderstood that not necessarily all such objects or advantages may beachieved in accordance with any particular embodiment of the invention.Thus, for example, those skilled in the art will recognize that theinvention may be embodied or carried out in a manner that achieves oroptimizes one advantage or group of advantages as taught herein withoutnecessarily achieving other objects or advantages as may be taught orsuggested herein.

Moreover, although this invention has been disclosed in the context ofcertain preferred embodiments and examples, it will be understood bythose skilled in the art that the present invention extends beyond thespecifically disclosed embodiments to other alternative embodimentsand/or uses of the invention and obvious modifications and equivalentsthereof. In addition, while a number of variations of the invention havebeen shown and described in detail, other modifications, which arewithin the scope of this invention, will be readily apparent to those ofskill in the art based upon this disclosure. For example, it iscontemplated that various combination or subcombinations of the specificfeatures and aspects of the embodiments may be made and still fallwithin the scope of the invention. Accordingly, it should be understoodthat various features and aspects of the disclosed embodiments can becombined with or substituted for one another in order to form varyingmodes of the disclosed invention. Thus, it is intended that the scope ofthe present invention herein disclosed should not be limited by theparticular disclosed embodiments described above, but should bedetermined only by a fair reading of the claims that follow.

1. A method for determining changes in a reactant supply system that isdesigned to supply repeated pulses of a vapor phase reactant to areaction chamber, the method comprising: providing a reactant source;providing a gas conduit system to connect the reactant source to thereaction chamber; providing a valve positioned in the gas conduit systemsuch that switching of the valve induces vapor phase reactant pulsesfrom the reactant source to the reaction chamber; repeatedly switchingthe valve to induce repeated vapor phase reactant pulses; providing afirst sensor that is in communication with the conduit system andprovides a first signal indicative of a first characteristic parameterof the reactant pulses as a function of time; generating a first curvehaving a shape from the first signal for the repeated reactant pulses;and monitoring the shape of the first curve to determine changes in theshape of the first curve over time, the changes in the shape of thefirst curve being indicative of changes in a supply of repeated reactantpulses to the reaction chamber.